Subcritical Water Hydrolysis Treatment of Waste Biomass for Nutrient Extraction

Nutrients were extracted from corn stalks, peanut shells, de-oiled peanut meal, chicken manure, and sewage sludge by a subcritical water (SCW) hydrolysis reaction. Compared with the other feedstock, the aqueous phases extracted from de-oiled peanut meal showed the highest watersoluble organic carbon, amino acid, total nitrogen, and phosphorus contents. The effects of solution pH, final hydrothermal temperature, and reaction time on nutrient extraction from de-oiled peanut meal were investigated. The analysis showed that alkaline reagents promoted liquefaction. The highest yield of the total primary nutrients (82.6%) was obtained with extraction reaction at 180 °C for 1.5 h using 0.1 mol/L KOH. The liquid fraction from this reaction was investigated for its potential use as a fertilizer with germination experiments. A higher germination index and root activity were obtained using the liquid extract with the appropriate dilution. These results indicated that subcritical water hydrothermal treatment is a viable way to recover nutrients from biomass wastes. In addition, de-oiled peanut meal is a suitable feedstock for the production of nutrient-rich liquid extract.